Signal discriminator

ABSTRACT

A signal discriminator is provided which leverages variation of permittivity of Mn—Zn-based ferrite. The signal discriminator comprises a soft magnetic material which has a capacitive reactance C, and which has its complex relative permittivity varying with frequency such that the real part ε′ of the complex relative permittivity is large in a low frequency domain and small in a high frequency domain. In the reactance component X 2 , the capacitive reactance C is not negligible with respect to the inductive reactance L in a low frequency domain, in consequence of which the value of the reactance component X 2  as a parallel circuit of the capacitive reactance C and the inductive reactance L is caused to decrease, and the influence of the capacitive reactance C is decreased in a high frequency domain. Consequently, the reactance component X 2  decreases more than the reactance component X 1  of a conventional soft magnetic material, and the X-R cross-point frequency moves to a frequency lower than a conventional X-R cross-point frequency XR 1 , whereby noises in a frequency band where noise components exist are converted into thermal energy thus reducing the waveform distortion originating from high frequency noises.

FIELD OF THE INVENTION

The present invention relates to a signal discriminator, andparticularly to a signal discriminator which has an excellent noiseblocking characteristic, and which is free from waveform distortion.

DESCRIPTION OF THE RELATED ART

As electronic devices are coming out with a reduced dimension and anenhanced performance, it is becoming increasingly important to reduceradiation noise coming from a cable, such as a signal line and a powerline, and conduction noise getting in the cable and conductingtherethrough. FIG. 8 shows a signal discriminator that is conventionallyand generally used to provide the simplest and easiest way forsuppressing such noises. Referring to FIG. 8, the signal discriminatorcomprises a cylindrical or toroidal magnetic core 2, and an insulator 3to cover the magnetic core 2, and is attached on a cable 1, such as asignal line or a power line, such that the cable 1 passes through themagnetic core 2. The cylindrical or toroidal magnetic core 2 may bestructured by a single piece 2 as shown in FIG. 9(a), or alternativelyby two pieces 2 a and 2 b as shown in FIG. 9(b), so as to form a closedmagnetic path.

FIGS. 10(a) and 10(b) show characteristic performance curves onpermeability μ and impedance Z, respectively, as a function offrequency, which are achieved by such a magnetic core as formed of asoft magnetic material. The magnetic core realizes high frequency noiseabsorbing effect (to be described later) in a high frequency band due toa pure resistance component (R) attributable to imaginary permeability(μ″), and therefore is favorably used as a signal discriminator todiscriminate signals from noises.

The impedance Z of the magnetic core having the characteristicsdescribed above is conventionally expressed by the permeability μ asfollows:Z=R+jX  (Formula 1)μ=μ′+jμ″  (Formula 2)where X is a reactance component which is generated by a real part μ′ ofthe permeability μ, and which is proportional to inductance, and R is aresistance component which is generated by an imaginary part μ″ of thepermeability μ, and which is composed of winding resistance, iron loss,and the like. As described later, the X and R components actuallyinclude winding-to-winding capacitance and core-to-winding capacitance,respectively.

Referring to FIG. 10(a), the permeability μ is expressed by the realpart μ′ and the imaginary part μ″. The real part μ′ decreases in a highfrequency band thus losing a nature as inductance, while the imaginarypart μ″ starts increasing at a certain frequency, hits its maximum vale,and then starts decreasing. The imaginary part μ″ functions as a pureresistance component in a signal discriminator, thus signals or noisesin a high frequency band are consumed as thermal energy.

Referring to FIG. 10(b), the reactance component X is dominant in a lowfrequency band, and the imaginary part μ″ increases in a high frequencyband thus causing the resistance component R to be dominant. Thereactance component reflects noises, and the resistance componentconverts noises into thermal energy.

The reactance component X reflects a noise in a cable toward an inputside of the cable thereby preventing the noise from further conductingin the cable, but the reflected noise may possibly constitute a sourceof other noises developing into radiation noises. On the other hand, theresistance component R consumes a noise by converting the noise intothermal energy, thus preventing development of any further noises.Accordingly, noses are preferably removed by a method of conversion intothermal energy.

A frequency, at which the values of the reactance component X and theresistance component R are equal to each other, is called “an X-Rcross-point frequency”, and in case of signal discriminators having thesame impedance characteristic, one thereof having a lower X-Rcross-point frequency is more effective in reducing noises. In order toachieve frequency characteristics as shown by FIGS. 10(a) and 10(b), amagnetic core is conventionally formed of Ni—Zn-based ferrite which hasa high resistivity. The Ni—Zn-based ferrite, however, is costly due toits raw material containing Ni, which results in an increased cost of asignal discriminator.

On the other hand, Mn—Zn-based ferrite is inexpensive but commonly has aresistivity as low as 0.1 to 1 Ωm due to electron transfer occurringbetween Fe³⁺ and Fe²⁺ (between ions), and eddy current loss startsincreasing already in a low frequency band, which results in that theMn—Zn ferrite practically works up to several hundred kHz at the utmost.At a frequency domain exceeding the several hundred kHz, the Mn—Znferrite has its permeability (initial permeability) significantlylowered thus completely losing characteristic as a soft magneticmaterial. Also, for prevention of insulation failure attributable to thelow resistivity, a cover or insulating coat is required resulting inincreased cost.

In order to solve the aforementioned problem, for example, JapanesePatent Application Laid-Open No. H05-283223 teaches a signaldiscriminator using a magnetic core which is formed of a comparativelyinexpensive Ni-free material (Mn—Zn-based ferrite) under a conventionalgeneral manufacturing process. The magnetic core thus formed is not onlyinexpensive but also achieves frequency characteristic on permeabilityand impedance substantially equivalent to that of a conventionalexpensive Ni—Zn-based magnetic core, thus an economical signaldiscriminator is provided. The aforementioned magnetic core contains asits main components: (a) 20 to 35 mol % MgO, (b) 10 to 20 mol % ZnO, (c)3 to 10 mol % MnO, and (d) 40 to 50 mol % Fe₂O₃; and as additives: (e) 0to 2 (0 excluded) weight % CuO, Bi₂, and O₃, respectively.

However, the solution described above involves the following problem.Since a conventional Ni—Zn-based magnetic core has a high resistivityand has an excellent high frequency characteristic, the resonantfrequency of a coil is high, and the X-R cross-point frequency is tofound to range from 10 MHz upward. Consequently, if the conventionalNi—Zn-based magnet core is applied to an input signal cable in a highinput impedance circuit, such as a C-MOS inverter, having anelectrostatic capacitance of several pF, a digital signal suffersringing, undershoot, or overshoot due to a high Q (reciprocal number ofloss coefficient) of the circuit, and a signal waveform is distorted.Here, since the magnetic core disclosed in the aforementioned JapanesePatent Application Laid-Open No. H05-283223 is made so as to obtainpermeability and impedance with frequency characteristic substantiallyequivalent to that of the conventional Ni—Zn-based magnetic core asdescribed above, the signal waveform distortion problem associated withthe conventional Ni—Zn-based magnetic core is found also in theaforementioned magnetic core. Further, since the magnetic core isinferior to other magnetic materials in magnetic characteristics such assaturation flux density, the magnetic core must have an increaseddimension in order to achieve an equivalent characteristic as a signaldiscriminator. Especially, when it is applied to a power line in which alarge current flows, and when ripple current or surge noise becomes aproblem, the magnetic core must have its dimension further increased inorder to prevent magnetic saturation.

The present invention has been made in light of the above problem, andit is an object of the present invention to provide a signaldiscriminator, which leverages the variation in the permittivity ofMn—Zn-based ferrite to thereby achieve an impedance characteristicequivalent to that of a signal discriminator formed of a conventionalNi—Zn-based magnetic core, and which also is highly resistant in a highfrequency noise band so as to reduce waveform distortion attributable tohigh frequency noise.

SUMMARY OF THE INVENTION

As described above, the impedance Z of the conventional magnetic core isexpressed by the aforementioned Formulas 1 and 2. On the other hand, itis noted in “Ceramic substrate for electronic circuit” (Pages 200 to201) by Electronic Materials Manufacturers Association of Japan that amagnetic substrate can be treated purely as a magnetic material when anelectrostatic field alone acts on it, but exhibits not only a magneticproperty but also a dielectric property when high frequency electric andmagnetic fields act on it simultaneously like microwave. Further, it isnoted that the permittivity of ferrite can reach an order of severalthousands at a low frequency (in kHz band and lower), and that mostferrites go beyond dispersion phenomenon in a frequency band rangingfrom 1 MHz upward, and many ferrites have their permittivity measuringsomewhere between 10 to 15 in a microwave band.

The present inventors, et al., with attention focused on the facts notedabove, increased the resistivity of a magnetic core formed of acomparatively inexpensive soft magnetic material not containing Ni,etc., and arranged that the real part of complex relative permittivityis large in a frequency band lower than the frequency of an electricsignal flowing in the cable and small in a frequency band higher thanthe frequency of the electric signal, and that a conventional generalmanufacturing process can be applied. As a result, it happens even inthe magnetic core formed of comparatively inexpensive soft magneticmaterial free of Ni, etc. that the eddy current loss in a signalfrequency band can be reduced by increase of resistivity, and also thatthe resistance component as the signal discriminator can be small in alow frequency band and large in a frequency band of the noise signal dueto the complex relative permittivity varying with the change offrequency, thus enabling reduction of waveform distortion arising fromthe high frequency noise.

Specifically, in order to achieve the object described above, accordingto claim 1 of the present invention, in a signal discriminator which isformed of a soft magnetic material to form a closed magnetic path, isattached on a cable such that the cable passes through the closedmagnetic path, and which passes an electric signal flowing through thecable and blocks a noise signal flowing through the cable, the softmagnetic material has its complex relative permittivity varying withfrequency, and a real part of the complex relative permittivity is largein a frequency domain lower than a frequency of the electric signalflowing through the cable and small in a frequency domain higher thanthe frequency of the electric signal.

According to claim 2 of the present invention, in the signaldiscriminator as described in claim 1, the real part of the complexrelative permittivity of the soft magnetic material may range from 1,000up to 20,000 at 1 kHz, and from 50 downward at 1 MHz.

According to claim 3 of the present invention, in the signaldiscriminator as described in claim 1 or 2, the soft magnetic materialmay be Mn—Zn ferrite having a basic component composition comprising44.0 to 50.0 (50.0 excluded) mol % Fe₂O₃, 4.0 to 26.5 mol % ZnO, 0.1 to8.0 mol % at least one of TiO₂ and SnO₂, and the rest consisting of MnO.

According to claim 4 of the present invention, in the signaldiscriminator as described in claim 1 or 2, the soft magnetic materialmay be Mn—Zn ferrite having a basic component composition comprising44.0 to 50.0 (50.0 excluded) mol % Fe₂O₃, 4.0 to 26.5 mol % ZnO, 0.1 to8.0 mol % at least one of TiO₂ and SnO₂, 0.1 to 16.0 mol % CuO, and therest consisting of MnO.

According to claim 5, in the signal discriminator as described in anyone of claims 1 to 4, the soft magnetic material may have a resistivityof 150 Ωm or higher.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) shows frequency characteristics for explanation of migrationof an X-R cross-point frequency;

FIG. 1(b) shows an equivalent circuit of a signal discriminator;

FIG. 2 shows component compositions (unit: mol %) of inventive samplemagnetic cores formed of soft magnetic materials according toembodiments of the present invention, and of comparative sample magneticcores formed of other soft magnetic materials;

FIG. 3 shows actual measurements of basic characteristics on the samplemagnetic cores comprising the component compositions (unit: mol %) shownin FIG. 2;

FIG. 4 shows frequency characteristics of real parts ε′ of complexrelative permittivity on Samples 1, 2, 3 and 4;

FIG. 5 shows changes of impedance Z on signal discriminators constitutedby Samples 1 to 5;

FIG. 6 shows impedance Z on Sample 1 split into a reactance component X2and a resistance component R;

FIG. 7 shows impedance Z on Sample 4 split into a reactance component X1and a resistance component R;

FIG. 8 shows a general signal discriminator attached on a cable;

FIGS. 9(a) and 9(b) explain general cylindrical or toroidal magneticcore structures to form a closed magnetic path, wherein FIG. 9(a) showsa single piece structure, and FIG. 9(b) shows a two piece structure; and

FIGS. 10(a) and 10(b) show characteristic curves of permeability μ andimpedance Z, respectively, on a magnetic core formed of a soft magneticmaterial.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As described above, a magnetic core formed of a soft magnetic material,such as ferrite, exhibits not only a magnetic property but also adielectric property, and has its permittivity varying with thefrequency. Consequently, the impedance Z expressed by the aforementionedFormula 1 is affected by permittivity ε. The magnetic core formed of thesoft magnetic material according to the present invention will bediscussed in view of not only permeability μ but also permittivity ε.

The permittivity ε is defined as follows:ε=ε′−jε″  (Formula 3)where ε′ is a real part of the permittivity ε, and ε″ is an imaginarypart of the permittivity ε.

As is clear from FIG. 10(b), if the resistance component R produced bythe imaginary part μ″ of the permeability μ moves toward a lowerfrequency, then the X-R cross-point frequency moves toward a lowerfrequency, too. The X-R cross-point frequency is caused to move also dueto a change in the configuration of the frequency characteristic of thereactance component X.

The present invention leverages the mechanism that the frequencycharacteristic of the reactance component X changes under the influenceof the permittivity ε in a low frequency band, and thereby the X-Rcross-point frequency moves toward a lower frequency.

In FIG. 1(a) showing frequency characteristics of the ε′, R and X, andexplaining migration of the X-R cross-point frequency, the abscissa axisrepresents frequency, and the ordinate axis represents impedance splitinto reactance components X1 and X2, a resistance component R, and realparts ε′1 and ε′2 of permittivity. The X1 is a reactance component incase of the real part ε′ of permittivity staying constant and small(ε′1), while the X2 is a reactance component in case of the real part ε′of permittivity changing in such a manner as to be large in a lowfrequency band and small in a high frequency band (ε′2). And, XR1 andXR2 are X-R cross-point frequencies defined by the resistance componentR crossing the reactance components X1 and X2, respectively.

Referring to FIG. 1(b), a signal discriminator is represented by aparallel circuit comprising a resistance component R and an inductivereactance L, and a capacitive reactance C. The capacitive reactance Cconsists of stray capacitance between winding wires, and straycapacitance between a core and wires. The stray capacitance between acore and wires depends on the real part of the permittivity of the coresuch that when the real part of the permittivity is large, thecapacitive reactance C is large. In the soft magnetic material accordingto the present invention, the capacitive reactance C depends on the realpart of the permittivity, and the complex relative permittivity varieswith frequency such that its real part is large in a frequency domainlower than the frequency of an electric signal flowing in a cable andsmall in a frequency domain higher than the aforementioned frequency.

Accordingly, in the reactance component X2, the capacitive reactance Cis not negligible with respect to the inductive reactance L in a lowfrequency domain, in consequence of which the value of the reactancecomponent X2 as the parallel circuit of the capacitive reactance C andthe inductive reactance L is caused to decrease (change inconfiguration). On the other hand, in a high frequency domain, theinfluence of the capacitive reactance C is decreased, and consequentlythe reactance component X2 decreases more than the reactance componentX1 without considerably changing the impedance characteristic as awhole, and the X-R cross-point frequency moves to the XR2 which is lowerthan the XR1.

As described above, in the signal discriminator according to the presentinvention, the frequency characteristic of the reactance component X ischanged through the influence of the permittivity ε, whereby the X-Rcross-point frequency is caused to move toward a low frequency, andnoises in a frequency band where noise components exist are convertedinto thermal energy thus reducing the waveform distortion originatingfrom high frequency noises.

Examples 1 and 2 will hereinafter be described. FIG. 2 shows basiccomponent compositions (unit: mol %) of inventive sample magnetic coresformed of soft magnetic materials according to Examples 1 and 2, andcomparative sample magnetic cores formed of other soft magneticmaterials for comparison purpose. Specifically, S1 indicates Sample 1according to Example 1, S2 indicates Sample 2 according to Example 2,and S3, S4 and S5 indicate Samples 3, 4 and 5, respectively.

In the examples described below, it is assumed that a signal frequencyis 1 MHz band, a frequency of noises to be removed is 10 to 500 MHzband, and that the X-R cross-point frequency to discriminate between thesignal frequency and the noise frequency is from 10 MHz downward, andresistivity p, which is to be determined by a voltage applied to acable, such as a signal line and a power line, is set at 150 Ωm whichfalls within a range where problems are kept off at an anticipatedvoltage in normal applications. Under the aforementioned assumption,basic component compositions are set so that the real part ε′ of thecomplex relative permittivity of a soft magnetic material ranges from1,000 up to 2,000 at 1 kHz, and from 50 downward at 1 MHz.

The reason the real part ε′ of the complex relative permittivity isadapted to range from 1,000 to 20,000 at 1 kHz is that if it is under1,000, the capacitive reactance C is too small thus failing to cause theconfiguration of the frequency characteristic of the reactance X tochange, and that if it is over 20,000, then the capacitive reactance Cis too large thus causing the reactance X to remarkably change to theextent of making an impact on the entire impedance characteristic. And,the reason the real part ε′ of the complex relative permittivity isadapted to range from 50 downward at 1 MHz is that if it is over 50, thecapacitive reactance C is too large in a high frequency band thuscausing the impedance characteristic to deteriorate in a high frequencyband.

EXAMPLE 1

Sample 1 has a basic component composition as shown by S1 in FIG. 2,specifically 47.0 mol % Fe₂O₃, 10.5 mol % ZnO, 1.0 mol % TiO₂, and 41.5mol % MnO, which falls within a proposed composition range of 44.0 to50.0 (50.0 excluded) mol % Fe₂O₃, 4.0 to 26.5 mol % ZnO, 0.1 to 8.0 mol% at least one of TiO₂ and SnO₂, and the rest consisting of MnO.Material powders Fe₂O₃, ZnO, TiO₂, and MnO as main componentspre-weighed for a predetermined ratio as shown by S1 in FIG. 2 weremixed by a ball mill to produce a mixture, and the mixture was calcinedat 900 degrees C. for 2 hours in the atmosphere. The mixture calcinedwas pulverized by a ball mill into particles with a grain diameteraveraging about 1.4 μm. Then, the mixture pulverized was mixed withpolyvinyl alcohol added, was granulated, and press-molded under apressure of 80 MPa into a green compact of a toroidal magnetic core witha post-sinter dimension of 15 mm in outer diameter, 8 mm in innerdiameter, and 3 mm in height. The green compact was sintered at 1,150degrees C. for 3 hours in an atmosphere with its oxygen partial pressurecontrolled by pouring in nitrogen.

Example 2

Sample 2 has a basic component composition as shown by S2 in FIG. 2,specifically 47.0 mol % Fe₂O₃, 10.5 mol % ZnO, 0.5 mol % SnO₂, 1.5 mol %CuO, and 39.5 mol % MnO, which falls within a proposed materialcomposition of 44.0 to 50.0 (50.0 excluded) mol % Fe₂O₃, 4.0 to 26.5 mol% ZnO, 0.1 to 8.0 mol % at least one of TiO₂ and SnO₂, 0.1 to 16.0 mol %CuO, and the rest consisting of MnO. Material powders Fe₂O₃, ZnO, SnO₂,CuO, and MnO as main components pre-weighed for a predetermined ratio asshown by S2 in FIG. 2 were mixed by a ball mill to produce a mixture,and the mixture was calcined at 900 degrees C. for 2 hours in theatmosphere. The mixture calcined was pulverized by a ball mill intoparticles with a grain diameter averaging about 1.4 μm. Then, themixture pulverized was mixed with polyvinyl alcohol added, wasgranulated, and press-molded under a pressure of 80 MPa into a greencompact of a toroidal magnetic core with a post-sinter dimension of 15mm in outer diameter, 8 mm in inner diameter, and 3 mm in height. Thegreen compact was sintered at 1,150 degrees C. for 3 hours in anatmosphere with its oxygen partial pressure controlled by pouring innitrogen.

Samples 3, 4 and 5 for comparison purpose have respective basiccomponent compositions as shown by S3, S4 and S5 in FIG. 2. Materialpowders selected out of Fe₂O₃, ZnO, NiO, MgO, CuO, and MnO as maincomponents and pre-weighed for respective predetermined ratios as shownby S3, S4, and S5 in FIG. 2 were mixed by a ball mill to producerespective mixtures, and the respective mixtures were calcined at 900degrees C. for 2 hours in the atmosphere. The respective mixturescalcined were pulverized by a ball mill into particles with a graindiameter averaging about 1.4 μm. Then, the respective mixturespulverized were mixed with polyvinyl alcohol added, were granulated, andpress-molded under a pressure of 80 MPa into respective green compactsof toroidal magnetic cores each with a post-sinter dimension of 15 mm inouter diameter, 8 mm in inner diameter, and 3 mm in height. The greencompact intended for Sample 3 was sintered at 1,150 degrees C. for 3hours in an atmosphere with its oxygen partial pressure controlled bypouring in nitrogen, while the green compacts intended for Samples 4 and5 were sintered at 1,150 degrees C. for 3 hours in the atmosphere.

FIG. 3 shows actual measurements of the basic characteristics of themagnetic cores formed with the basic component compositions shown inFIG. 2. The symbols S1 to S5 in FIG. 3 correspond respectively to S1 toS5 in FIG. 2. The actual measurements include: initial permeability μiat 0.1 MHz; saturation magnetic flux density Bs at 1,194 A/m;resistivity ρv; and real parts ε′ of complex relative permittivity at 1kHz and 1 MHz, respectively.

Referring to FIG. 3, while Samples 1 and 2, and Sample 4 of Ni—Zn-basedferrite are satisfactory in all of initial permeability μi, saturationmagnetic flux density Bs, and resistivity ρv, Sample 3 of conventionalgeneral Mn—Zn-based ferrite is satisfactory in initial permeability μi,and saturation magnetic flux density Bs, but has a remarkably lowresistivity ρv therefore preventing its usage in a high frequency band.Also, since the remarkably low resistivity ρv of Sample 3 requireseither that a thin insulating coat be provided on the surface of themagnetic core or that a cable on which the magnetic core is attached beinsulated, its application is limited. And, Sample 5 of Mg—Zn-basedferrite has a low saturation magnetic flux density Bs and therefore doesnot have an advantage over the other samples. Since a signaldiscriminator is especially required to be prevented from becomingmagnetically saturated by a ripple current and a surge noise, Sample 5with a low saturation magnetic flux density Bs must have an increaseddimension.

Referring to FIG. 4, Samples 1 and 2 have the real parts ε′ of complexrelative permittivity measuring over 10,000 at 1 kHz, but decreasing at5 kHz upward and measuring about 30 at 1 MHz. Sample 3 of generalMn—Zn-based ferrite has the real part ε′ of complex relativepermittivity measuring over 100,000 at 1 kHz, about 2,000 at 1 MHz, andstill over 1,000 at 10 MHz. And, Sample 4 of Ni—Zn-based ferrite has thereal part ε′ of complex relative permittivity measuring as low as about20 even at 1 kHz.

Referring to FIG. 5 where the abscissa axis represents frequency, andthe ordinate axis represents impedance, Sample 3 has its impedancecharacteristic significantly deteriorating compared with the othersamples in a frequency band from 10 MHz upward, that is a frequencyrange crucial to anti-noise measures in the examples of the presentinvention where it is assumed that a signal frequency is 1 MHz band, anda noise frequency is 10 to 500 MHz band. This happens becauseMn—Zn-based ferrite for Sample 3 has a low resistivity ρv, and also hasthe real part ε′ of complex relative permittivity measuring over 100,000at 1 kHz, about 2,000 at 1 MHz, and still over 1,000 at 10 MHz.

Referring to FIG. 6 showing the impedance Z on the aforementioned Sample1 split into a reactance component X2 and a resistance component R,Sample 1 has its X-R cross-point frequency XR2 1 falling atapproximately 5 MHz. Sample 2 has substantially the same characteristicas Sample 1 shown in FIG. 6.

Referring to FIG. 7 showing the impedance Z on the aforementioned Sample4 split into a reactance component X1 and a resistance component R,Sample 4 has its X-R cross-point frequency XR1 falling at approximately10 MHz, which is the same as conventionally.

Samples 1 and 2 have their X-R cross-point frequency falling at 5 MHzbecause Samples 1 and 2 have the real part ε′ of complex relativepermittivity measuring over 10,000 at 1 kHz but decreasing from 5 kHzupward to measure about 30 at 1 MHz.

Thus, it is proved that Samples 1 and 2 according to the presentinvention have better impedance characteristic and noise reducingperformance than Sample 3 of conventional Mn—Zn-based ferrite, Sample 4of Mg—Zn-based ferrite, and Sample 5 of Ni—Zn-based ferrite.

INDUSTRIAL APPLICABILITY

According to claim 1 of the present invention, in a signal discriminatorwhich is formed of a soft magnetic material to form a closed magneticpath, is attached on a cable such that the cable passes through theclosed magnetic path, and which passes an electric signal flowingthrough the cable and blocks a noise signal flowing through the cable,the soft magnetic material has its complex relative permittivity varyingwith frequency, and the real part of the complex relative permittivityis large in a frequency domain lower than a frequency of the electricsignal flowing through the cable and small in a frequency domain higherthan the frequency of the electric signal, whereby the signaldiscriminator is enabled to suppress noise components while passingsignal components.

According to claims 2 to 5 of the present invention, a low-cost signaldiscriminator is obtained which is adapted for a signal frequency of 1MHz band, removes noises in a frequency of 10 to 500 MHz, has an X-Rcross-point frequency of 10 MHz and below, and which discriminatessignals from noses without magnetic saturation, and with goodinsulation.

1. A signal discriminator which is formed of a soft magnetic material toform a closed magnetic path, is attached on a cable such that the cablepasses through the closed magnetic path, and which passes an electricsignal flowing through the cable and blocks a noise signal flowingthrough the cable, characterized in that the soft magnetic material hasits complex relative permittivity varying with frequency, and a realpart of the complex relative permittivity is large in a frequency domainlower than a frequency of the electric signal flowing through the cableand small in a frequency domain higher than the frequency of theelectric signal.
 2. A signal discriminator according to claim 1, whereinthe real part of the complex relative permittivity of the soft magneticmaterial ranges from 1,000 up to 20,000 at 1 kHz, and from 50 downwardat 1 MHz.
 3. A signal discriminator according to claim 1, wherein thesoft magnetic material is Mn—Zn ferrite having a basic componentcomposition comprising 44.0 to 50.0 (50.0 excluded) mol % Fe₂O₃, 4.0 to26.5 mol % ZnO, 0.1 to 8.0 mol % at least one of TiO₂ and SnO₂, and therest consisting of MnO.
 4. A signal discriminator according to claim 1,wherein the soft magnetic material is Mn—Zn ferrite having a basiccomponent composition comprising 44.0 to 50.0 (50.0 excluded) mol %Fe₂O₃, 4.0 to 26.5 mol % ZnO, 0.1 to 8.0 mol % at least one of TiO₂ andSnO₂, 0.1 to 16.0 mol % CuO, and the rest consisting of MnO.
 5. A signaldiscriminator according to claim 1, wherein the soft magnetic materialhas a resistivity of 150 Ωm or higher.
 6. A signal discriminatoraccording to claim 2, wherein the soft magnetic material is Mn—Znferrite having a basic component composition comprising 44.0 to 50.0(50.0 excluded) mol % Fe₂O₃, 4.0 to 26.5 mol % ZnO, 0.1 to 8.0 mol % atleast one of TiO₂ and SnO₂, and the rest consisting of MnO.
 7. A signaldiscriminator according to claim 2, wherein the soft magnetic materialis Mn—Zn ferrite having a basic component composition comprising 44.0 to50.0 (50.0 excluded) mol % Fe₂O₃, 4.0 to 26.5 mol % ZnO, 0.1 to 8.0 mol% at least one of TiO₂ and SnO₂, 0.1 to 16.0 mol % CuO, and the restconsisting of MnO.
 8. A signal discriminator according to claim 2,wherein the soft magnetic material has a resistivity of 150 Ωm orhigher.
 9. A signal discriminator according to claim 3, wherein the softmagnetic material has a resistivity of 150 Ωm or higher.
 10. A signaldiscriminator according to claim 4, wherein the soft magnetic materialhas a resistivity of 150 Ωm or higher.